The objectives of the proposed research are threefold. First, experiments will be continued to determine the role of divalent cations in transmitter release from presynaptic nerve terminals, using the neuromuscular junction of the frog. The preparations will be treated with divalent ion ionophore in calcium free solution. Calcium and other divalent ions will then be applied to the presynaptic terminal by iontophoresis and the resulting transmitter release monitored by recording from the muscle end-plate. Second, experiments will be done to define further the properties of acetylcholine receptors in eel electroplaque by applying acetylcholine to the cell iontophoretically under voltage clamp conditions and determining the effects of changes in ionic composition of the bathing solution on the resulting synaptic currents. Third, experiments will be continued on the effects of postganglionic axotomy on synaptic transmission in the ciliary ganglion of the chick. Physiological and morphological studies will be done to determine the factors contributing to the loss of synaptic transmission after the postganglionic axons have been severed.